(1) Field of the Invention
The present invention relates to a process for the production of an elemental material, comprising the step of reacting a halide of the elemental material with a reducing material in solid form in a fluidized bed reactor at a reaction temperature which is below the melting temperature of the reducing material. In a preferred embodiment of the present invention, the elemental material is titanium and the titanium is produced in powder form. The invention also relates to the production of alloys and intermetallic compounds of the elemental materials.
(2) Description of Related Art
The Kroll process and the Hunter process are the two present day methods of producing titanium commercially. In the Kroll process, titanium tetrachloride is chemically reduced by magnesium at temperatures between 800 and 900° C. The process is conducted in a batch fashion in a metal (steel) retort with an inert atmosphere (usually helium or argon). Magnesium is charged into the vessel and heated to prepare a molten magnesium bath. Liquid titanium tetrachloride at room temperature is dispersed dropwise above the molten magnesium bath. The liquid titanium tetrachloride vaporizes in the gaseous zone above the molten magnesium bath. A reaction occurs on the molten magnesium surface to form titanium and magnesium chloride. The Hunter process is similar to the Kroll process, but uses sodium instead of magnesium to reduce the titanium tetrachloride to titanium metal and produces sodium chloride as a by-product. For both processes, the reaction is uncontrolled and sporadic and promotes the growth of dendritic titanium metal. The titanium fuses into a mass that encapsulates some of the molten magnesium (or sodium) chloride. This fused mass is called titanium sponge. After cooling of the metal retort, the solidified titanium sponge metal is broken up, crushed, purified either by vacuum distillation or acid leach and then dried in a stream of hot nitrogen. Metal ingots are made by compacting the sponge, welding pieces into an electrode and then melting it into an ingot in a high vacuum arc furnace. High purity ingots require multiple arc melting operations.
Powder titanium is usually produced from the sponge through grinding, shot casting or centrifugal processes. A common technique is to first react the titanium with hydrogen to make brittle titanium hydride to facilitate the grinding process. After formation of the powder titanium hydride, the particles are dehydrogenated to produce a usable metal powder product. The processing of the titanium sponge into a usable form is difficult, labor intensive, and increases the product cost by a factor of two to three.
The processes discussed above have several intrinsic problems that contribute heavily to the high cost of titanium production. Both processes are batch processes and batch process production is inherently capital and labor intensive. The processes also suffer from low productivity because the reactor has to be charged, heated, and discharged, which involves a long down time between batches. Furthermore, due to the batch nature of these processes, there is significant quality variation in the titanium metal produced from batch to batch. Additionally, the titanium sponge produced by these processes requires further substantial processing to produce titanium in a usable form; thereby increasing cost, increasing hazard to workers and exacerbating batch quality control difficulties. In addition, both processes are energy intensive and neither process utilizes the large exothermic energy reaction, requiring substantial energy input for titanium production (approximately 6 kW-hr/kg product metal).
The titanium tetrachloride used in the commercial production of titanium metal is usually obtained by chlorinating relatively high-grade titanium dioxide ore, which also partially contributes to the high cost of the metal. Chlorination of lower grade ores such as ilmenite, synthetic rutile, and slag, which has been developed by the TiO2 pigment manufacturers, greatly reduces the cost of TiCl4.
The reduction of titanium tetrachloride to metal has been attempted using a number of reducing agents including hydrogen, carbon, sodium, calcium, aluminum and magnesium. As discussed above, both the magnesium and sodium reduction of titanium tetrachloride have proved to be commercial methods for producing titanium metal. However, also as discussed above, the current commercial methods use batch processing, which is undesirable.
The greatest potential for decreasing the production cost associated with the commercial production of titanium metal is the development of a continuous reduction process with attendant reduction in material handling. There is a strong demand for both the development of a process that enables continuous economical production of titanium metal and for the production of metal powder suitable for use, without additional processing, for application to powder metallurgy or for vacuum-arc melting to ingot form.